Operating members for snap-action switches

ABSTRACT

An operating member, and method of producing same, for reciprocation within a close-fitting bore of a snap-action switch, the member including a guide pin having a hollow, deepdrawn shank portion with a consequential high-quality external finish thereto, an end portion of the guide pin comprising an increased-diameter shoulder forming the boundary of an insulating button moulded thereto and preventing deposition of the insulating material on the shank portion during the moulding process.

trite State's atent 1 1 McAlpine 1, 1973 [s41 OPERATING MEMBERS FOR SNAP- 2,040,919 5/1936 Caldwell ..200/159 B ACTION SWITCHES 2,221,868 11/1940 Geiger et 31.... ....339/218 L x 2,439,886 4/1948 Denmark ....339/218 L x lnventorI Ewest McAlrme, B111 Quay, 2,448,808 9/1948 Koch ..339/218 L x Gateshead, England [73] Assignee: Burgess Micro Switch Company Limited, Durham, England 22 Filed: Mar. 1, 1972 21 Appl. No.: 230,591

[30] Foreign Application Priority Data Mar. 3, 1971 Great Britain ..5,884/7l [52] U.S. Cl. ..200/l72 R, 339/218 R [51] Int. Cl. ..H0lh 3/02 [58] Field ofSearch ..200/l72 R, 163; 339/218 R, 218 L, 218 M [56] References Cited UNITED STATES PATENTS 2,023,190 12/1935 Alden ..339/2l8LX Primary Exdminer-Robert K. Schaefer Assistant Examiner-William J. Smith Alt0rneyErnest A. Greenside et a1.

[57] ABSTRACT An operating member, and method of producing same, for reciprocation within a close-fitting bore of a snap-action switch, the member including a guide pin having a hollow, deep-drawn shank portion with a consequential high-quality external finish thereto, an end portion of the guide pin comprising an increaseddiameter shoulder forming the boundary of an insulating button moulded thereto and preventing deposition of the insulating material on the shank portion during the moulding process.

4 Claims, 3 Drawing Figures OPERATING MEMBERS FOR SNAP-ATION SWITCHES This invention relates to operating members for snap-action switches, for example to such members having a metal guide pin carrying a button of insulating material, the guide pin reciprocating within a closely fitting bore to actuate a snap-acting switch mechanism In order to ensure that the switch always snaps over at the same depressed position of the operating member it is essential that the close fit of the guide pin in its bore is maintained throughout the life of the switch. Thus the external surface of the guide pin should have as high a quality finish as possible.

Heretofore, guide pins have been formed from stainless steel, either turned or ground. To assemble the operating member, the pin is located in a close fitting bore formed in the first part of a mould, to rest on an ejector member in said bore, which member accurately determines the location of the pin in mould with its upper, pre-formed end projecting from the bore. The mould is completed by a second part, and the insulating material is injected into the mould to form the button about the pre-formed upper end-of the pin.

In practice it has been found difficult to prevent flash of moulded insulating material from travelling from the mould cavity along the shank portion of the guide pin because of the construction of the completed operating member and the wear of the mould which necessarily occurs. Thus, the finished operating member must be subjected to a de-flashing operation which tends to cause damage to the surface of the shank portion of the member, in turn, adversely affecting the performance of the member in the associated switch. Clearly, with a shank portion reciprocating in, for example, a moulded phenolic bore, any roughness in the surface of the shank portion will produce premature wear of the phenolic bore.

According to the present invention there is provided an operating member for a snap-action switch, comprising a hollow guide pin including a deep-drawn shank portion and an increased diameter end portion, a button of insulating material being moulded to the end portion, and a region of the end portion being disposed ton, a region of said end portion being disposed between the shank portion and the insulating material to form an external surface of the operating member thereat.

Thus the invention provides an operating member with a shank portion having a particularly smooth external surface, and one which is less likely to require the performance of a de-flashing operation than heretofore.

By way of example only, an operating member and a method of production thereof, according to the invention will now be described in greater detail with reference to the accompanying drawings of which:

FIG. 1 is a vertical section through an operating member,

FIG. 2 is a vertical section through a mould for producing the member of FIG. I, with a guide pin in position, and

FIG. 3 illustrates an alternative shape of guide pin.

Referring to the drawings, the operating member comprises a hollow guide pin 2 of stainless steel, the pin including a deep-drawn cylindrical shank portion 4 closed at one end. Formed integrally with the shank portion 4 in the drawing operation is an increaseddiameter end region indicated generally at 5 and combetween the shank portion and the insulating material to form an external surface of the operating member thereat.

At least a peripheral part of said region of the end portion may be adapted to provide a boundary of said external surface remote from the shank portion by abutment with a surface of the mould during the moulding process thereby to prevent the deposition on said external surface and shank portion of the insulating material of said button. Preferably said peripheral part comprises an annular projection surrounding the associated end region of the shank portion.

Advantageously the end portion further includes an extension which provides keying means for the moulded insulating material.

A method of producing an operating memberaccording to the invention comprises the steps of deepdrawing the shank portion of said guide pin, supporting the guide pin in a first part of a mould with the shank portion located in a bore in said first part, closing the mould with a second part, and moulding the insulating material to the end portion of the pin to form said butprising an annular shoulder 6, depending below and surrounding the upper end of the shank portion 4, and an obliquely inturned peripheral extension 8. This extension can conveniently be turned inwards in a final stage of the deep-drawing operation using a suitably shaped female die member.

' Moulded to the guide pin 2, and keyed to it by the extension 8, is a button 10 of insulating material, for example a phenolic resin. The annular shoulder 6 provides a boundary for the material of the button so that the moulded bottom surface of the button terminates well clear of the shank portion 4. The moulding material fills the bore of the shank portion 4 thereby increasing the strength of the guide pin.

Referring more particularly to FIG. 2, a mould used in producing the operating member comprises upper and lower parts 12, 14 respectively. The lower part 14 contains a vertical bore 16 in which the preformed, deep-drawn shank portion 4 is positioned, the annular shoulder 6 of the guide pin resting on the upper surface of the mould part 14-.

The upper part 12 of the mould is formed to provide the required shape of button 10 and, on closure of the mould, the insulation material is injected to fill the cavity formed thereby as well as the hollow extent of the shank portion 4. Thus it can be seen that the abut- .ment of the shoulder 6 with the surface of the mould part 14 forms a boundary for the insulating material andprevents any of said material being deposited on the shank portion 4 during the moulding process. As mentioned above, the extension 8 provides a key for the insulating material during the moulding process. Although the extension 8 illustrated in FIGS. l and 2 is inclined inwardly, it is possible to locate this extension at other angles within the material of the button, for example as shown in FIG. 3 with the extension 8 inclined outwardly.

On completion of the moulding process, and after removal of the upper part R2 of the mould, the finished operating member is ejected from the lower part 14 by means of the pin 18 in the bore 16.

It is to be noted that the distance from the bottom face of the button and the end of the shank portion 4, which will usually be a critical dimensions, is determined by the guide pin sizing, quite independently of the moulding operation. This is in contrast to known arrangements in which a turned guide pin has to be supported by the ejector pin 18 at a given position before the button is moulded, so that the moulded bottom surface can be correctly spaced from the end of the guide pin shank.

Moreover, since the shoulder 6 forming a boundary for the moulded bottom face of the button is at some distance from the bore carrying the shank portion 4, wear of the bore, and in particular any deterioration of the upper edge 22 of the bore, does not affect the final production. It will be clear, also, that there is now no need for the shank portion to be a sealing fit in the bore. That the moulded material is kept well clear of bore, a function enhanced by the line-contact seal provided by the shoulder 6, obviates or minimizes any deflashing of the member after the moulding operation.

A result of forming the pin shank by a deep-drawing process is to provide an extremely smooth external surface to the shank portion 4, any irregularities of profile extending axially of the pin and therefore less likely to cause wear on reciprocation of the pin within a receiving bore than would a turned or ground shank portion as has heretofore been used, which has circumferentially directed surface irregularities. The reduced wear in turn means that there will be less dust within the switch casing by deposition of material worn away from the wall of the bore receiving the pin, so that one cause of malfunctioning after prolonged use is removed. It should also be pointed out that in contrast to operating members having turned pins, the resultant design is also lighter and is more economical to produce.

What I claim and desire to protect by Letters Patent 1. An operating member for a snap-action switch and comprising a hollow guide pin including a deep-drawn shank portion and an increased diameter end portion, and a button of insulating material moulded to said end portion, a region of said end portion between the shank portion and the insulating material forming part of the external surface of the operating member.

2. An operating member as claimed in claim 1 in which said region of the end portion includes a peripheral part adapted to provide a boundary of said part of the external surface remote from the shank portion by abutment with a surface of a mould during the moulding process.

3. An operating member as claimed in claim 2 in which said peripheral part comprises an annular projection surrounding the associated end region of the shank portion.

4. An operating member as claimed in claim 1 in which the end portion includes an extension adapted to provide keying means for said moulded insulating material. 

1. An operating member for a snap-action switch and comprising a hollow guide pin including a deep-drawn shank portion and an increased diameter end portion, and a button of insulating material moulded to said end portion, a region of said end portion between the shank portion and the insulating material forming part of the external surface of the operating member.
 2. An operating member as claimed in claim 1 in which said region of the end portion includes a peripheral part adapted to provide a boundary of said part of the external surface remote from the shank portion by abutment with a surface of a mould during the moulding process.
 3. An operating member as claimed in claim 2 in which said peripheral part comprises an annular projection surrounding the associated end region of the shank portion.
 4. An operating member as claimed in claim 1 in which the end portion includes an extension adapted to provide keying means for said moulded insulating material. 